The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

Motorists urged to take care on NSW roads

NSW Roads Minister Duncan Gay has urged motorists to take extra care while driving home from their long weekend break, after the deaths of five people on the state's roads.

The toll is more than double last year's total of two, Mr Gay said in a statement, imploring motorists to be extremely careful when driving home on Monday.

"Motorists should drive to the conditions, take plenty of breaks and avoid driving when they would normally be sleeping," he said.

He said speeding was the biggest killer, with 40 per cent of crashes each year involving excessive speed.

"There is no excuse for speeding and motorists who ignore the road rules, especially during double demerit periods, risk losing their licence," Mr Gay said.

His call came after a 77-year-old woman was killed on Sunday after veering to the wrong side of the road and crashing into a road train near Griffith in the state's south.

During the long weekend safety campaign, Operation Stay Alert, motorists are reminded that double demerits remain in force until midnight (AEST) on Monday night for speeding, seatbelt and helmet offences.